Dentists, surgeons and other professionals use various surgical telescopes or magnification loupes to create a magnified image of the visual field. Most, but not all, of these devices are on-axis units, meaning that the eyepiece and objective share the same axis. To accommodate for this straight-axis vision, the user must assume an unfavorable posture involving a combination of head and back bend and/or excessive eye tilt. These conditions frequently result in back and/or neck pain and eye strain, all of which intensify with prolonged use. Such neck, back and eye problems afflict a high percentage of dentists, surgeons and people in various other occupations where head and eye tilt are essential to view the operating area well below the normal, horizontal view.
The mounting of the majority of magnifying optics provides a fixed downward tilt from the horizontal vision of a surgeon or dentist, standing or sitting in an upright position, and requires eye tilt in use. Most magnifying optics require eye tilt of between 10° and 34°, while some are as extreme as 45°. Eye strain is proportional to eye tilt and prolonged eye tilt greater than 25° can lead to significant eye strain. Eye tilt of 22.5° or less has been found to be acceptable and does not result in undue eye strain for the user.
As noted in U.S. Pat. 5,923,467, granted Pericic et al. on Jul. 13, 1999:                When performing surgery, for example, a surgeon relies on a high level of eye hand co-ordination generally with a small margin for error and so to enhance the precision and accuracy of the surgery it is necessary to magnify the region of the operation. Operating optical microscopes which comprise optical devices mounted on fixed stands have been used by surgeons for this purpose. However the field of view of these microscopes is set at the beginning of an operation and is not easily reset if a surgeon needs to alter the field of view to gain a better perspective of the operation or of the operating region.        It is also common for surgeons to wear small head mounted binoculars or loupes to magnify their field of view. However as the level of an operation is below the normal level of eyesight of the surgeon, the head of the surgeon must be inclined to enable him to watch and co-ordinate his hands. During long operations even a slight inclination of the head can overwork the muscles of the neck discomforting the surgeon and providing an additional unnecessary distraction. This problem is compounded by the weight of the head mounted loupes.        To allow a surgeon to sit and concentrate in one position for a long length of time and reduce the stress on the muscles of the neck it is preferable that the head and neck of the surgeon be in an upright aligned position so that the surgeon's line of sight is straight ahead. However due to the level of an operation this position is not possible with existing loupes.        Furthermore this problem is not exclusively confined to those in the surgical profession. In fact any person such as a jeweller who is using existing loupes and manipulating very small objects for any length of time will encounter the same problems associated with inclination of the head, as the surgeon.        
Many experts believe ergonomic factors should be the major selection criteria for devices to be used by dentists and surgeons in performing their work. Most dentists and surgeons with ideal posture and ergonomic position require a viewing angle relative to straight-ahead viewing of between 55° and 75° for the vast majority of procedures. This viewing angle range is desired with or without telescopes, loops or magnifying optics in the viewing path.
B. J. Chang, Ph.D. and President of Surgitel Systems, a division of General Scientific, Corp., is greatly concerned and is interested in preventing chronic neck and back problems for dental care providers. He has authored articles and presented lectures focusing on the importance of correct viewing angles for dentists. The viewing angle determines neck and back posture and Dr. Chang calls it the most important ergonomic factor. “Most telescopes, due to their limited declination angles, are not very ergonomic and may actually cause excessive head tilt and neck pain,” Chang warns.
Dr. David Ahearn, president of Design/Ergonomics, states, “Loupes can be part of the problem in terms of neck pain and in terms of overall flexibility of treatment.”
Several designs have taken steps to provide a means of placing combinations of mirrors or prisms between the objective and eyepiece to attempt to resolve the problem. Pericic et al. discloses a single Schmidt prism which changes the path of the image by 45° after passing through the objective. This device is utilized with the operator looking straight ahead (horizontally), even though the ability of the user to see over the device with normal, unmagnified vision is essential in practical use. If one tips this device down far enough to see over it, the resultant viewing angle deviation is too great for the majority of applications.
Others have used mirrors and various prisms to redirect the incoming light path, but many are too large to be practical. Devices with mirror/prism attachments located beyond or anterior to the magnifying optics or the telescope unit exist, but these units are heavy to the user. One reason for this is the leverage which exists due to extending the deflector anteriorly. This creates more force on the supporting device of the user. The Lyst et al. (U.S. Pat. No. 6,120,145) is an example of such a design, which employs path deviating prisms and/or reflectors beyond the magnifying optics. Some prism or mirror units are designed to be used without magnification, such as the device disclosed in U.S. Pat. No. 6,280,031 by Zerkle. This device provides a 90° viewing angle change.
None of the prior art devices, including those disclosed in the Pericic et al. and Lyst et al. Patents, have the essential features of an ideal Prism for Ergonomic Position or ideal viewing angle deflector.